High purity indium and manufacturing method therefor

ABSTRACT

Provided is high purity Indium having a purity of 7N (99.99999%) or higher, and containing 0.05 ppm or less of Pb, 0.005 ppm or less of Zn, and 0.02 ppm or less of S. A method of producing high purity In, wherein SrCO 3  is added to an electrolyte upon performing electrolytic refining using 5N (99.999%) In to reduce Pb, Zn and S to attain a purity of 7N (99.99999%) or higher. Under circumstances where In demands for LED, such as InGaN and AlInGaP, are anticipated, it is necessary to produce indium in mass quantities and inexpensively, and the present invention provides technology capable of achieving the same.

BACKGROUND

The present invention provides high purity indium (In) having a purity of 7N or higher which is particularly useful as a raw material of indium phosphide (InP), and a method of producing such high purity In, and particularly relates to a method of producing high purity In via electrolytic refining which enables the production of high purity In less expensively than conventional technologies.

Generally speaking, a high purity raw material is used for producing a compound semiconductor monocrystal such as InP as one type of a group III-V semiconductor, and dry methods such as distillation and zone refining are adopted as the methods of producing high purity In for refining the raw material to be from 4N to 6N or higher, and the following Patent Documents can be listed as examples.

Patent Document 1 below describes performing distillation at 1250° C., Patent Document 2 describes performing zone melting after baking, Patent Document 3 describes reacting the raw material with chlorine gas and performing distillation thereto, and subjecting indium chloride to disproportionation reaction with distilled water, and as a special example Patent Document 4 describes a method of continuously casting distilled In.

Meanwhile, upon reviewing the conventional technologies related to wet refining, Patent Document 5 describes a refining method of In. The specific disclosure of Patent Document 5 is as follows.

Note that the representation of the unit “ppm” used in this specification means “wtppm” in the ensuing explanation.

Coarse In containing less than 10 ppm of Cd and less than 1 ppm of Tl is used as the raw material, and this raw material is used as the anode and electrolytic refining is performed in a hydrochloric acid bath at an In concentration of 100 to 300 g/L, pH of 0.5 to 2, and current density of 0.5 to 2 A/dm².

Electrolytic refining is performed by separating the anode chamber and the cathode chamber with a diaphragm, and, after the electrolysis, the electrolyte of the anode chamber is extracted and filtered, and thereafter caused to come into contact with anion exchange resin to perform solution purification. Furthermore, impurities that are nobler than In in the electrolyte are removed via electrolysis at a current density of 0.3 to 2.5 A/dm², and the resultant product is supplied to the cathode chamber and subject to electrolytic refining.

As materials of the diaphragm, exemplified are natural fibers such as cotton, fabrics made from synthetic fiber such as polyethylene, polypropylene, and polyester, and non-woven fabrics, and materials having sufficiently small through holes are considered preferable, and in the Examples Tetoron filter cloth is used.

As the filter, Patent Document 5 describes that any material capable of filtration will suffice, and in the Examples a cartridge filter is used.

Nevertheless, Patent Document 5 entails a problem in that expensive anion exchange resin needs to be used, and a problem in that electrolysis needs to be performed for removing impurities for the solution purification of electrolyte.

Patent Document 6 below describes a refining method of In. This is considered to be an improvement of Patent Document 5 described above. In the Examples, the purity is 4 to 5N, but Patent Document 6 uses coarse In containing more impurities than Patent Document 5 as the raw material, and uses such raw material as the anode and performs electrolytic refining in a hydrochloric acid bath at an In concentration of 100 to 200 g/L, pH of 1.5 to 2.5, and current density of 0.5 to 2 A/dm².

Electrolytic refining is performed by separating the anode chamber and the cathode chamber with a diaphragm, and, after the electrolysis, the electrolyte of the anode chamber is extracted, and thereafter caused to come into contact with anion exchange resin to perform solution purification. Furthermore, impurities that are nobler than In in the electrolyte are removed via electrolysis at a current density of 0.3 to 2.5 A/dm² and by causing the metal In and the electrolyte to come into contact, and the resultant product is supplied to the cathode chamber and subject to electrolytic refining. Moreover, Patent Document 6 describes a method of supplying In ions to the electrolyte by performing diaphragm electrolysis using a ceramic filter or the like.

As materials of the diaphragm, exemplified are natural fibers such as cotton, fabrics made from synthetic fiber such as polyethylene, polypropylene, and polyester, and non-woven fabrics, and materials having sufficiently small through holes are considered preferable, and in the Examples Tetoron filter cloth is used.

As the filter, Patent Document 6 describes that any material capable of filtration will suffice, and in the Examples a cartridge filter is used.

Nevertheless, Patent Document 6 entails the same problems as Patent Document 5; namely, a problem in that expensive anion exchange resin needs to be used, and a problem in that electrolysis needs to be performed for removing impurities for the solution purification of electrolyte.

Patent Document 7 below describes high purity metal In and its production method and usage. The specific disclosure of Patent Document 7 is as follows.

Two-stage electrolytic refining is performed, and refining is performed by blowing inert gas upon casting the electrodeposited In obtained from the two-stage electrolytic refining and thereby eliminating residual volatile matter. The purity attained in Patent Document 7 is described as being “6N level”.

Electrolysis may be performed in either a hydrochloric acid bath or a sulfuric acid bath, In concentration of 20 to 80 g/L and pH of 1.0 to 2.5 are preferable, and a diaphragm is not used. The total current density of the first electrolysis and the second electrolysis is 100 to 500 A/m² (1 to 5 A/dm²), and the current density of the second electrolysis is set to be lower than the current density of the first electrolysis. By adding Na hydroxide or a mixture of Na hydroxide and Na nitrate as the flux during casting, Cl is caused to be 0.03 ppm or less, and S is caused to be 0.01 ppm or less.

Example 1 shows the results when inert gas is not blown, Example 2 shows the results when inert gas is blown, and Examples 3 to 5 show the results when the flux is used to blow inert gas. Patent Document 7 entails a problem in that the cost will increase since electrolysis is performed in two stages, and a problem in that the process is complicated because it is necessary to perform casting for preparing an anode between the first stage and the second stage.

Patent Document 8 describes a refining method of In including a step of extracting the electrolyte from the anode chamber and filtering the extracted electrolyte, and causing the electrolyte to come into contact with the anion exchange resin, and a step of supplying the electrolyte to the cathode chamber of the electrolytic solution purification bath in which the anode chamber and the cathode chamber are separated with a diaphragm and performing electrolytic solution purification. In this case also, Patent Document 8 entails a problem in that expensive anion exchange resin needs to be used, and a problem in that electrolysis needs to be performed for removing impurities for the solution purification of electrolyte. Furthermore, the purity level that can be attained in Patent Document 8 is merely 6N level.

Patent Document 9 describes dissolving an In inclusion in hydrochloric acid, adding alkali to this solution and performing neutralization so that pH will become a predetermined value within the range of 0.5 to 4, precipitating and eliminating predetermined metal ions in the solution as hydroxide, subsequently blowing hydrogen sulfide gas thereon to precipitate and eliminate metal ions that are harmful for the electrolysis in the subsequent process as sulfides, and thereafter subjecting the In metal to electrolytic refining with this solution as the electrolytic solution.

Patent Document 9 describes that, based on this method, it is possible to recover In having a purity of 99.999% or higher from ITO target scraps. Nevertheless, in the foregoing case, it is only possible to recover In having a purity level of 5N.

Patent Document 10 discloses a method of producing high purity strontium carbonate which is used in the present invention described later, and is also listed as a reference.

PRIOR ART DOCUMENTS Patent Documents [Patent Document 1] Japanese Patent Application Publication No. 2002-212647

[Patent Document 2] Japanese Patent Application Publication No. H04-026728 [Patent Document 3] Japanese Patent Application Publication No. H01-156437 [Patent Document 4] Japanese Patent Application Publication No. H10-121163 [Patent Document 5] Japanese Patent Application Publication No. H01-031988 [Patent Document 6] Japanese Patent Application Publication No. H01-219186

[Patent Document 7] Japanese Patent Application Publication No. 2005-179778

[Patent Document 8] Japanese Patent Application Publication No. S64-31988

[Patent Document 9] Japanese Patent Application Publication No. 2007-131953

[Patent Document 10] Japanese Patent Application Publication No. H9-77516

SUMMARY

An object of the present invention is to provide high purity In having a purity of 7N or higher which is particularly useful as a raw material of InP, and a method of producing such high purity In, as well as provide a method of producing high purity In via electrolytic refining which enables the production of high purity In less expensively than conventional technologies. Under circumstances where In demands for LED, such as InGaN and AlInGaP, are anticipated, it is necessary to produce indium in mass quantities and inexpensively, and the present invention provides technology capable of achieving the same.

Based on the above, the present application provides the following invention.

In the present invention, excluding C (carbon), N (nitrogen), and O (oxygen) as the gas constituent components, the analytical values of the concentration of the respective elements are values that were analyzed based on GDMS (Glow Discharge Mass Spectrometry).

(1) High purity In containing 0.05 ppm or less of Pb, 0.005 ppm or less of Zn, and 0.02 ppm or less of S, and having a purity of 7N (99.99999%) or higher.

(2) The high purity In according to (1) above, wherein the high purity In contains 0.001 ppm or less of Fe, less than 0.01 ppm of Sn, and less than 0.005 ppm of Si.

Moreover, the present application provides the following invention.

(3) A method of producing high purity In via electrolysis, wherein 5N (99.999%) In is used as a raw material, SrCO₃ is added to an electrolyte upon performing electrolytic refining using the raw material to reduce Pb content in the electrolyte, and electrodeposited In is separated from a negative plate and cast in an atmosphere or an oxygen-containing gas atmosphere to attain a purity of 7N (99.99999%) or higher.

(4) The method of producing high purity In according to (3) above, wherein an anode solution (anolyte) and a cathode solution (catholyte) are partitioned with a diaphragm having a gas permeability of 5 cm³/cm² sec or less, and the electrolyte in contact with a cathode is refined by being preliminarily filtered with a filter having fine pores of 0.5 μm or less.

(5) A method of producing high purity In via electrolytic refining, wherein electrolytic refining is performed by partitioning an anode solution (anolyte) and a cathode solution (catholyte) with a diaphragm having a gas permeability of 5 cm³/cm² sec or less, extracting a part of the catholyte into a catholyte tank that is different from an electrolytic bath and adding SrCO₃ to the catholyte in the catholyte tank to eliminate Pb in the catholyte, passing the catholyte with Pb eliminated therefrom through and filtering the catholyte with a filter having fine pores of 0.5 μm or less, and circulating and supplying the filtered catholyte so as to return the catholyte once again into a cathode box in the electrolytic bath.

(6) The method of producing high purity In according to any one of (3) to (5) above, wherein sulfuric acid is used as the electrolyte, and electrolysis is performed at a pH of 0.5 to 1.5.

Moreover, the present application provides the following invention.

(7) The method of producing high purity In according to any one of (3) to (6) above, wherein electrolysis is performed at a current density of 1 to 5 A/dm².

(8) The method of producing high purity In according to any one of (3) to (7) above, wherein electrolysis is performed under conditions in which an In concentration in the electrolyte is 65 to 120 g/L and a Cl concentration in the electrolyte is 6 to 10 g/L.

(9) The method of producing high purity In according to any one of (3) to (8) above, wherein refining is performed upon adding 0.1 to 2.0 g/L of SrCO₃.

(10) A method of producing high purity In, wherein high purity In produced with the electrolytic refining method of high purity In according to any one of (3) to (9) above is separated from a negative plate and cast in an atmosphere or an oxygen-containing gas atmosphere at a temperature of 170 to 190° C.

(11) A method of producing high purity In produced with the electrolytic refining method of high purity In according to any one of (3) to (10) above containing 0.05 ppm or less of Pb, 0.005 ppm or less of Zn, and 0.02 ppm or less of S, and having a purity of 7N (99.99999%) or higher.

The present invention yields superior results in being able to provide high purity In having a purity of 7N or higher which is particularly useful as a raw material of InP, and a method of producing such high purity In. Moreover, the production method via electrolytic refining of the present invention enables the production of high purity In less expensively than conventional technologies. Demands for LED, such as InGaN and AlInGaP, are increasing drastically, and it is necessary to produce indium in mass quantities and inexpensively, and the present invention provides technology capable of achieving the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram of an electrolytic bath that is used in the production of high purity In via a electrolytic refining according to the present invention.

DETAILED DESCRIPTION

In order to facilitate the understanding of the present invention, details of the experiments are explained.

Previously, In as the raw material of an InP compound semiconductor was refined, for instance, based on a dry method of subjecting 4N In to baking (1000° C.) and distillation (1050° C.) to attain a purity level of 6N. Nevertheless, the dry method entails high equipment costs and manufacturing costs, and, in order to mass-produce high purity In of 7N or higher, the baking process and the distillation process need to be repeated a plurality of times, and enormous capital investment is required. Thus, the present inventors examined whether high purity In for use as InP could be obtained based on wet refining.

Moreover, while certain conventional technologies describe a purity level of 6N or higher, in reality it was only possible to attain 6N level In, and higher purification was required. The present inventors set the target purity to 7N or higher, and conducted experiments of electrolytic refining using a sulfuric acid bath.

The production of high purity In via electrolytic refining of the present invention is performed using the device as shown in FIG. 1. To explain FIG. 1, a titanium (Ti) metal plate to be used as a negative plate is disposed in an electrolytic bath (electrolytic bath), and an In ingot having a purity of 5N is placed in an anode. A cathode box comprising a filter cloth that functions as a diaphragm is disposed between the cathode and the anode so as to partition both electrode plates.

Here, the standard of pores of the filter cloth is standardized as gas permeability in JIS L1096, and the present invention uses a filter cloth having a gas permeability of 5 cm³/cm² sec or less at 124.5 Pa, and thereby prevents impurities such as suspended matter in the anolyte from getting mixed into the catholyte.

Furthermore, a catholyte tank is disposed outside the electrolytic bath, a part of the electrolyte in the cathode box is introduced into the catholyte tank, and SrCO₃ is added therein.

As a result of performing the foregoing processes, lead (Pb) contained in the catholyte is settled at the bottom of the catholyte tank as PbCO₂—O—CO₂Sr, and the catholyte with Pb eliminated therefrom is returned to the cathode box within the electrolytic bath so that the catholyte with Pb eliminated therefrom can be circulated and used.

Here, the catholyte with Pb eliminated therefrom in the catholyte tank is filtered and refined by being passed through a filter having pores of 0.5 μm or less so as to prevent the inclusion of Pb in the cathode box. The pores of the filter are more preferably 0.2 μm.

With regard to the In raw material, 5N (99.999%) In is used as the anode. 5N level In can be easily produced by independently performing the distillation method, and a commercially available material may be used.

The main impurities of the 5N In produced by independently performing the distillation method described above are Pb (lead), Zn (zinc), and Sn (tin), and in particular Pb is contained in an amount of roughly 1 ppm. While electrolytic refining is able to reduce impurities such as Sn, Fe (iron), and Ni (nickel), the biggest problem is in the elimination of Pb, and a major challenge is to easily eliminate Pb.

Moreover, the present invention uses a sulfuric acid solution in the electrolytic refining process, and, while the content of S (sulfur) in the 5N In raw material based on the foregoing distillation method is 0.005 ppm, the S content increased to 0.05 ppm after electrolytic refining, and the reduction of the S content after electrolytic refining is required in order produce 7N In.

Furthermore, with regard to Zn also, the content of Zn in the 5N In raw material based on the foregoing distillation method is 0.1 ppm, and can be reduced to 0.05 ppm after electrolytic refining, but needs to be reduced further in order to produce 7N In.

Upon producing the high purity In of the present invention, 5N (99.999%) In is used and refining is performed via electrolysis, and Pb is reduced by adding SrCO₃ to the electrolyte in the catholyte tank of the device as shown in FIG. 1. This is a major feature of the present invention. Since the basis of this invention is electrolytic refining, the present invention is advantageous in being able to improve the productivity since it can be achieved at a cost that is ⅕ to ⅙ of the refining process based on the dry method.

Electrolytic refining is performed in a sulfuric acid solution, the cathode box is disposed so as to surround the periphery of the cathode, and a filter cloth is placed on the face of the cathode box opposing the anode plate so as to prevent the mixture of impurities in the anolyte and the catholyte.

As described above, this filter cloth has a gas permeability of 5 cm³/cm² sec or less, and more preferably 1 cm³/cm² sec or less. 5N In is disposed outside the cathode box that is inside the electrolytic bath. A catholyte tank is disposed outside the electrolytic bath, a part of the catholyte in the cathode box is introduced into the catholyte tank, and SrCO₃ is added therein.

Upon performing electrolysis, sulfuric acid is used as the electrolyte and electrolysis is performed at a pH of 0.5 to 1.5. This is because, when the pH is less than 0.5, the current efficiency will deteriorate due to the generation of hydrogen, and when the pH exceeds 1.5, the electrolytic voltage will increase.

Furthermore, electrolysis is performed at a current density of 1 to 5 A/dm². This is because, when the current density is less than 1 A/dm², the productivity will deteriorate, and when the current density exceeds 5 A/dm², the electrolytic voltage will increase. Moreover, dendrite tends to arise and impurities that are nobler than In tend to become precipitated in the cathode during the electrolytic refining.

During the electrolysis, the In concentration and the Cl concentration in the electrolyte (catholyte) that comes into contact with the cathode are, respectively, 65 to 120 g/L and 6 to 10 g/L. This is because, when the In concentration is less than 65 g/L, the current efficiency will deteriorate due to the generation of hydrogen particularly during electrolytic refining, and when the In concentration exceeds 120 g/L, the in-process inventory of expensive In will increase. When the Cl concentration is less than 6 g/L, the electrodeposition of In becomes precipitated on the dendrite and damages the diaphragm. Moreover, while there is no major problem even when the Cl concentration exceeds 10 g/L, this is undesirable since it will affect the corrosion of peripheral equipment and shorten the life of the device.

With regard to SrCO₃, 0.1 to 2.0 g/L of SrCO₃ is added to the catholyte in the catholyte tank, and Pb is settled at the bottom of the catholyte tank as PbCO₂—O—CO₂Sr. The catholyte in the catholyte tank with Pb settled at the bottom thereof is passed through a filer having pores of 0.5 μm or less so that it will not contain PbCO₂—O—CO₂Sr and then returned to the electrolyte in the cathode box so that the catholyte can be circulated and used.

As a result of the foregoing processes, since Pb²⁺ can be precipitated as PbCO₂—O—CO₂Sr and settled at the bottom of the catholyte tank by adding SrCO₃ to the catholyte in the catholyte tank, Pb in the electrolyte can be reduced, and Pb can thereby be eliminated from the In to be subject to electrolytic refining. When the concentration of SrCO₃ is less than 0.1 g/L, the Pb elimination effect will deteriorate, and when the concentration of SrCO₃ exceeds 2.0 g/L, the filter will become clogged, and the frequency of replacing the filter will increase.

Upon performing electrolytic refining based on the present invention, the raw material In to be used as the anode is dissolved in the electrolyte (anolyte). Under appropriate electrolysis conditions, impurities that are nobler than In will not become electrodeposited on the cathode, and will remain on the anode surface or get mixed into the electrolyte as fine suspended matter, and when they exist as suspended matter, there is a possibility that they may get mixed into In that is electrodeposited on the cathode. Accordingly, upon performing electrolytic refining, it is preferable to dispose a diaphragm with sufficiently small pores between the anode and the cathode.

(Electrode Reaction)

The cathode reaction is as follows:

In³⁺+3e→In

Filter cloth film

-   -   (Anode chamber)

In³⁺→In³⁺ (cathode chamber)

The anode reaction is as follows.

In→In³⁺+3e

(Trace amount) Pb→Pb²⁺+2e

-   -   (Catholyte chamber (tank))

Pb²⁺+SrCO₂—O—CO₂Sr→PbCO₂—O—CO₂Sr+Sr²⁺

As shown with the reaction of the catholyte chamber (tank) described above, when SrCO₃ is added, Pb²⁺ becomes precipitated as PbCO₂—O—CO₂Sr, and can thus be eliminated. The catholyte is further introduced into the catholyte tank, and In that eluted to the anolyte on the Ti electrode is precipitated, and In having a purity of 6N or higher can be obtained.

While the purities of SrCO₃ introduced into the catholyte tank are Si: 0.51 ppm, S: 4.9 ppm, Ca: 50 ppm, Fe<0.5 ppm, Ni<05 ppm, and Pb<0.1 ppm, since they are diluted in the catholyte, the actual amounts that get mixed into In will decrease as shown in the Examples described later. Since the technique of purifying SrCO₃ is disclosed in Patent Document 10 described above (Japanese Patent Application Publication No. H9-77516), high purification can be easily achieved.

In other words, based on the foregoing production method, it is possible to obtain high purity In containing 0.05 ppm or less of Pb, 0.005 ppm or less of Zn, and 0.02 ppm or less of S, and having a purity of 6N (99.9999%) or higher.

Furthermore, it is also possible to obtain high purity In containing 0.001 ppm or less of Fe, less than 0.01 ppm of Sn, and less than 0.005 ppm of Si.

While FIG. 1 shows an example of using sulfuric acid, when electrolytic refining is performed in a hydrochloric acid bath and the generation of chlorine gas from the anode is to be prevented, an anode box may be disposed so as to cause the anode to come into contact with sulfuric acid as with the In recovery method via electrowinning of Japanese Patent Application Publication No. H08-060264 (Patent No. 3089595, Nippon Mining & Metals Co., Ltd.).

After electrolysis, the electrodeposited In is separated from the cathode, and melt and cast at 170 to 190° C. to prepare an ingot. By performing the melting and casting process in the atmosphere or an oxygen-containing gas atmosphere, oxides of Zn and S are formed and are separated and eliminated from In in the form of solids or gases. Consequently, the Zn content in In can be reduced to 0.005 ppm or less, and the S content in In can be reduced to 0.01 ppm or less. Note that, as the oxygen-containing gas, mixed gas of high purity argon and high purity oxygen or oxygen enriched air may be used.

EXAMPLES

The Examples and Comparative Examples of the present invention are now explained.

Example 1

As Example 1, electrolytic refining using a sulfuric acid bath (using the device shown in FIG. 1) is now explained. A filter cloth having a gas permeability of 5 cm³/cm² sec or less was disposed between an anolyte and a catholyte separated with a cathode box to prevent impurities such as suspended matter existing in the anolyte from getting mixed into the catholyte. The electrolytic refining conditions were set as follows; specifically, In concentration in the catholyte: 80 g/L, pH: 1.2, SrCO₃: 0.5 g/L, current density: 3 A/dm², and Cl concentration in the catholyte: 8 g/L.

The impurity content of SrCO₃ added to the catholyte tank was as follows; specifically, Si: 0.51 ppm, S: 4.9 ppm, Ca: 50 ppm, Fe<0.5 ppm, Ni<05 ppm, and Pb<0.1 ppm.

Electrolytic refining was performed using SrCO₃ by adding SrCO₃ to the catholyte in the catholyte tank to attain a concentration of 0.5 g/L, passing the catholyte with Pb eliminated therefrom through and filtering the catholyte with a filter having fine pores of 0.5 μm or less, and circulating and supplying the filtered catholyte so as to return the catholyte once again into a cathode box in the electrolytic bath. The result of separating the electrodeposited In after the electrolytic refining from the Ti electrode plate of the cathode and analyzing the impurities is shown in Table 1.

Consequently, it was possible to reduce the impurities in the In after electrolytic refining as follows; specifically, Pb: 0.02 ppm, Sn: less than 0.01 ppm (less than detection limit), Ni: 0.006 ppm, and Fe: 0.001 ppm. Moreover, while it was also possible to reduce the Zn content to 0.05 ppm, with this content it was not possible to attain a 7N purity. Furthermore, while the S content was 0.005 ppm in a 5N In raw material produced via the distillation method, the S content increased to 0.05 ppm after performing electrolytic refining, and the S content needed to be reduced in order to produce 7N In.

Subsequently, the electrodeposited In after electrolytic refining was separated from the cathode plate, melted at 180° C., and cast in the atmosphere. Consequently, the impurity content in the In after casting was, as shown in Table 1, Na: 0.001 ppm, Si: less than 0.005 ppm (less than detection limit), Ca: 0.005 ppm, Fe: less than 0.001 ppm (less than detection limit), Ni: 0.002 ppm, Sn: less than 0.01 ppm (less than detection limit), and Pb: 0.02 ppm, and maintained at the content after electrolytic refining. In particular, with regard to Zn and S, they reacted with the oxygen in the atmosphere during casting and formed oxides, and in particular Zn formed oxides (slag) and became solid matter (suspended matter), and was separated and removed from the molten In. Moreover, S became sulfur oxide gas, and was separated and removed from the molten In. Consequently, Zn and S were reduced as follows; specifically, Zn: 0.005 ppm, and S: 0.01 ppm.

Moreover, in Example 1, since the concentration of other impurities such as Li, Be, B, F, Mg, Al, P, Cl, K, Sc, Ti, V, Cr, MN, Co, Cu, Ga, Ge, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ru, RH, Pd, Ag, Cd, Sb, Te, I, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Bi, Th, and U were all less than the GDMS detection limit, these elements are excluded. The same applies to the following Examples.

As a result of the above, it was possible to reduce all impurities via electrolytic refining and casting. In particular, the present invention use 5N In that was produced only through distillation as the anode raw material, but it was also possible to reduce the main impurities such as Pb, Zn, Sn, Fe, and Ni in the anode raw material as well as S and other impurities that get mixed in from the sulfuric acid solution used in the electrolytic refining process, and thereby produce 7N purity In. Moreover, the yield was 98% or higher in all cases.

TABLE 1 Unit: wtppm SrCO₃ concentration Casting in electrolyte temperature (g/L) (° C.) Na Si S Ca Fe Ni Zn Sn Pb Raw material — — 0.001 0.005 0.005 0.005 0.05 0.08 0.1 0.01 1.0 (5N- In) After electrolysis 0.5 — 0.006 <0.005 0.05 0.01 0.001 0.006 0.05 <0.01 0.02 After casting — 180 0.001 <0.005 0.01 0.005 <0.001 0.002 0.005 <0.01 0.02

Comparative Example 1

Next, as Comparative Example 1, electrolytic refining of In was performed under the same conditions as Example 1 other than eliminating the process of adding SrCO₃ to the catholyte in the catholyte tank of Example 1 described above, and casting was additionally performed at a molten metal temperature of 170° C.

The results are shown in Table 2. The In refined under the conditions of Comparative Example 1 had the following impurity content; specifically, Pb: 0.5 ppm, S: 0.03 ppm, and Zn: 0.02 ppm, and it was not possible to achieve a 7N purity. Meanwhile, it was possible to reduce the other impurities to the same content level as Example 1 (Na: 0.001 ppm, Si: less than 0.005 ppm (less than detection limit), Ca: 0.004 ppm, Fe: 0.001 ppm, Ni: 0.001 ppm, Sn: less than 0.01 ppm (less than detection limit)).

TABLE 2 Unit: wtppm SrCO₃ concentration Casting in electrolyte temperature (g/L) (° C.) Na Si S Ca Fe Ni Zn Sn Pb Raw material — — 0.001 0.005 0.005 0.005 0.05 0.08 0.1 0.01 1.0 (5N-In) After electrolysis 0.0 — 0.005 <0.005 0.05 0.01 0.001 0.006 0.05 <0.01 0.5 After casting — 170 0.001 <0.005 0.03 0.004 0.001 0.001 0.02 <0.01 0.5

Example 2

As Example 2, the electrolytic refining conditions were set as follows; specifically, additive concentration of SrCO₃ in the catholyte tank: 0.1 g/L, In concentration in the catholyte: 65 g/L, pH: 0.5, current density: 1 A/dm², and Cl concentration in the catholyte: 6 g/L. The major difference from Example 1 is that the additive concentration of SrCO₃ in the catholyte tank was set to be a lower concentration than Example 1.

The impurity content of SrCO₃ added to the catholyte tank was as follows; specifically, Si: 0.51 ppm, S: 4.9 ppm, Ca: 50 ppm, Fe<0.5 ppm, Ni<05 ppm, and Pb<0.1 ppm.

The results of the impurity concentration in In after performing electrolytic refining based on the foregoing conditions, and thereafter casting the electrodeposited In at 170° C. are shown in Table 3.

Consequently, the impurity content was Pb: 0.04 ppm, Zn: 0.005 ppm, and S: 0.01 ppm, and the concentration of other impurities was Na: 0.001 ppm, Si: less than 0.005 ppm (less than detection limit), Ca: 0.005 ppm, Fe: less than 0.001 ppm (less than detection limit), Ni: 0.002 ppm, and Sn: less than 0.01 ppm (less than detection limit). Moreover, impurities other than those described above were also analyzed with GDMS, but they were all less than the detection limit as with Example 1, and quantitative evaluation could not be performed. Accordingly, it was possible to produce In having a 7N purity.

As described above, it was possible to produce 7N In, and the yield was 98% or higher in all cases.

TABLE 3 Unit: wtppm SrCO₃ concentration Casting in electrolyte temperature (g/L) (° C.) Na Si S Ca Fe Ni Zn Sn Pb Raw material — — 0.001 0.005 0.005 0.005 0.05 0.08 0.1 0.01 1.0 (5N-In) After electrolysis 0.1 — 0.006 <0.005 0.05 0.01 0.001 0.006 0.05 <0.01 0.04 After casting — 170 0.001 <0.005 0.01 0.005 <0.001 0.002 0.005 <0.01 0.04

Example 3

As Example 3, the electrolytic refining conditions were set as follows; specifically, additive concentration of SrCO₃ in the catholyte tank: 2.0 g/L, In concentration in the catholyte: 120 g/L, pH: 1.5, current density: 5 A/dm², and Cl concentration in the catholyte: 10 g/L. The major difference from Examples 1 and 2 is that the additive concentration of SrCO₃ in the catholyte tank was set to be a higher concentration than Example 1.

The impurity content of SrCO₃ added to the catholyte tank was as follows; specifically, Si: 0.51 ppm, S: 4.9 ppm, Ca: 50 ppm, Fe<0.5 ppm, Ni<05 ppm, and Pb<0.1 ppm.

The results of the impurity concentration in In after performing electrolytic refining based on the foregoing conditions, and thereafter casting the electrodeposited In at 190° C. are shown in Table 4. Consequently, the impurity content was Pb: 0.01 ppm, Zn: 0.005 ppm, and S: 0.01 ppm, and the concentration of other impurities was Na: 0.001 ppm, Si: less than 0.005 ppm (less than detection limit), Ca: 0.005 ppm, Fe: less than 0.001 ppm (less than detection limit), Ni: 0.002 ppm, and Sn: less than 0.01 ppm (less than detection limit). Moreover, impurities other than those described above were also analyzed with GDMS, but they were all less than the detection limit as with Examples 1 and 2, and quantitative evaluation could not be performed. Accordingly, it was possible to produce In having a 7N purity.

As described above, it was possible to produce 7N In, and the yield was 98% or higher in all cases.

TABLE 4 Unit: wtppm SrCO₃ concentration Casting in electrolyte temperature (g/L) (° C.) Na Si S Ca Fe Ni Zn Sn Pb Raw material — — 0.001 0.005 0.005 0.005 0.05 0.08 0.1 0.01 1.0 (5N-In) After electrolysis 2.0 — 0.006 <0.005 0.05 0.01 0.001 0.006 0.05 <0.01 0.01 After casting — 190 0.001 <0.005 0.01 0.005 <0.001 0.002 0.005 <0.01 0.01

The present invention provides high purity In containing 0.05 ppm or less of Pb, 0.005 ppm or less of Zn, and 0.02 ppm or less of S, and having a purity of 7N (99.99999%) or higher, and additionally provides a method of producing high purity In, wherein SrCO₃ is added to an electrolyte upon performing electrolytic refining using 5N (99.999%) In to reduce Pb, Zn and S to attain a purity of 7N (99.99999%) or higher. Under circumstances where In demands for LED, such as InGaN and AlInGaP, are anticipated, it is necessary to produce indium in mass quantities and inexpensively, and the present invention provides technology capable of achieving the same.

In addition, in comparison to the dry refining method, since expensive equipment costs are not required and running costs can also be reduced, the present invention yields an effect of being able to reduce costs. 

1: High purity In containing 0.05 ppm or less of Pb, 0.005 ppm or less of Zn, and 0.02 ppm or less of S, and having a purity of 7N (99.99999%) or higher. 2: The high purity In according to claim 1, wherein the high purity In contains 0.001 ppm or less of Fe, less than 0.01 ppm of Sn, and less than 0.005 ppm of Si. 3: A method of producing high purity In via electrolysis, wherein 5N (99.999%) In is used as a raw material, SrCO₃ is added to an electrolyte upon performing electrolytic refining using the raw material to reduce Pb content in the electrolyte, and electrodeposited In is separated from a negative plate and cast in an atmosphere or an oxygen-containing gas atmosphere to attain a purity of 7N (99.99999%) or higher. 4: The method of producing high purity In according to claim 3, wherein an anode solution (anolyte) and a cathode solution (catholyte) are partitioned with a diaphragm having a gas permeability of 5 cm³/cm² sec or less, and the electrolyte in contact with a cathode is refined by being preliminarily filtered with a filter having fine pores of 0.5 μm or less. 5: A method of producing high purity In via electrolytic refining, wherein electrolytic refining is performed by partitioning an anode solution (anolyte) and a cathode solution (catholyte) with a diaphragm having a gas permeability of 5 cm³/cm² sec or less, extracting a part of the catholyte into a catholyte tank that is different from an electrolytic bath and adding SrCO₃ to the catholyte in the catholyte tank to eliminate Pb in the catholyte, passing the catholyte with Pb eliminated therefrom through and filtering the catholyte with a filter having fine pores of 0.5 μm or less, and circulating and supplying the filtered catholyte so as to return the catholyte once again into a cathode box in the electrolytic bath. 6: The method of producing high purity In according to claim 5, wherein sulfuric acid is used as the electrolyte, and electrolysis is performed at a pH of 0.5 to 1.5. 7: The method of producing high purity In according to claim 6, wherein electrolysis is performed at a current density of 1 to 5 A/dm². 8: The method of producing high purity In according to claim 7, wherein electrolysis is performed under conditions in which an In concentration in the electrolyte is 65 to 120 g/L and a Cl concentration in the electrolyte is 6 to 10 g/L. 9: The method of producing high purity In according to claim 8, wherein refining is performed upon adding 0.1 to 2.0 g/L of SrCO₃. 10: A method of producing high purity In, wherein high purity In produced with the electrolytic refining method of high purity In according to claim 9 is separated from a negative plate and cast in an atmosphere or an oxygen-containing gas atmosphere at a temperature of 170 to 190° C. 11: A method of producing high purity In produced with the electrolytic refining method of high purity In according to claim 10 containing 0.05 ppm or less of Pb, 0.005 ppm or less of Zn, and 0.02 ppm or less of S, and having a purity of 7N (99.99999%) or higher. 12: The method of producing high purity In according to claim 3, wherein sulfuric acid is used as the electrolyte, and electrolysis is performed at a pH of 0.5 to 1.5. 13: The method of producing high purity In according to claim 3, wherein electrolysis is performed at a current density of 1 to 5 A/dm². 14: The method of producing high purity In according to claim 3, wherein electrolysis is performed under conditions in which an In concentration in the electrolyte is 65 to 120 g/L and a Cl concentration in the electrolyte is 6 to 10 g/L. 15: The method of producing high purity In according to claim 3, wherein refining is performed upon adding 0.1 to 2.0 g/L of SrCO₃. 16: A method of producing high purity In, wherein high purity In produced with the electrolytic refining method of high purity In according to claim 3 is separated from a negative plate and cast in an atmosphere or an oxygen-containing gas atmosphere at a temperature of 170 to 190° C. 17: A method of producing high purity In produced with the electrolytic refining method of high purity In according to claim 3, wherein the high purity In contains 0.05 ppm or less of Pb, 0.005 ppm or less of Zn, and 0.02 ppm or less of S, and has a purity of 7N (99.99999%) or higher. 